I sort of see where you're coming from op but here's my experience of it.
I have 2ds's in the same school year.
ds1 has emotional, behavioral and social difficulties. He is very challenging but responds well to praise. At primary school he received rewards for what would seem very basic things and he received these as often as warranted this. He responds well to the rewards and praise. Others who received regular awards were often the high achievers.
ds2 was always average. He rarely received extra praise in the form of certificates etc, once a term probably, as was standard for each child to receive something at least once a term.
I always explained that his brother found it harder to do certain things so was rewarded more frequently for those things, he knew that because he was always reasnoably behaved and did his work he would have to push that little bot harder for recognition. He received regular praise in general from us and teachers whereas ds1 was regularly in trouble.
Fast forward to today.
ds1 is in a special school after struggling for many years. He will hopefully leave school with some basic qualifications and I hope he may be able to fit into society one day. He still receives lots of certificates and rewards for very basic things such as sitting through one 30 minute lesson. He is so proud of these achievements and rightly so, they are often the one or two positive things he can take from a day at school.
ds2 is in top sets throughout the board. He is expected A* - B's in his GCSE's and is a well respected member of school with both teachers and peers. A few years ago he was expected to be a B,C,D student but he has gone the extra mile in the last 18 months and pushed himself harder. This has been noticed by school and he has received the encouragement from staff recognising this. He is a very well-rounded young man and an absolute pleasure to be around.
I am immensely proud of them both as they have both come a long way individually.
Yes, primary school children are young and may not see the bigger picture but I do believe all experiences help to build us however young. As long as there is praise for all the children at some point.
It did break my heart to see ds2 without a certificate again on a Friday afternoon, I am only human! But I turned this into reassurance and encouragement and it helped him to understand his brother wasn't just naughty and annoying!
Oh and I was chair of PTA for many years but didn't see a change in treatment of ds's 